In the complete combustion of common gaseous fuels, the fuel combines with oxygen to produce carbon dioxide, water and heat. There can be intermediate reactions producing carbon monoxide and hydrogen. The heat, however, can also cause other chemical reactions such as causing atmospheric oxygen and nitrogen to combine to form oxides of nitrogen or NO.sub.x. While NO.sub.x may be produced in several ways, thermal NO.sub.x is associated with high temperatures, i.e. over 2800.degree. F. The flame is zoned so that different parts of the flame are at different temperatures. NO.sub.x production can be reduced with the lowering of the peak flame temperature. The reduction in NO.sub.x can be achieved through turbulence of the gases being combusted which introduces low temperature excess air and/or flue gases into the flame thus reducing the flame temperature.